In recent years, a storage system referred to as object storage which adopts a key-value store (KVS) storage interface with a host (client) is becoming widely used. In the KVS storage system, a write request from the host includes information of an identifier of write data, namely, information of a key, and write data, namely, data of a value (hereinafter referred to simply as value data). A read request from the host includes information of a key. As the key information, the storage system often uses a character string.
To improve the reliability of the storage system, it is necessary to use a highly reliable and expensive drive, and this leads to cost increase. In contrast, if an inexpensive drive is used, this not only causes performance penalties such as an increase in the downtime of the system and a decrease in the service performance of the system, but also causes increases in the cost for a replacement drive and in the operation cost of service personnel for drive replacement and rebuilding process.